1. Field of the Invention
The present invention relates in general to disk storage systems and more particularly, methods and apparatus for providing positional information on a disk in a hard drive assembly.
2. Description of the Related Art
Disk drives are magnetic recording devices used for the storage of information. The information is typically recorded on concentric tracks on either surface of one or more magnetic recording disks. To facilitate the storage and retrieval of data in an orderly manner, disks are typically organized in blocks called sectors. These sectors are located on the disk by a set of unique specifiers called cylinder (or track), head (or side) and sector number. The disks are rotatably mounted to a spin motor and information is accessed by means of read/write heads that are mounted to actuator arms which are rotated by a voice coil motor. The voice coil motor is excited with a current to rotate the actuator and move the heads. The read/write heads must be accurately aligned with the storage tracks on the disk to ensure proper reading and writing of information.
To accurately write and read data, it is desirable to maintain the head on the center of the track. To assist in controlling the position of the head, each sector of the disk typically contains a number of servo bits accurately located relative to the centerline of the track. The raw signals produced by the servo bits are typically demodulated into a position signal which is utilized by a servo system to determine the position of the head relative to the track, and to move the actuator arm if the head is not located on the track centerline.
Due to defects in the servo patterns, the read head does not return to its original position after one revolution, as shown in FIG. 1A. This results in a gap between the original (starting) position and the position of the read/write head after one revolution. The resulting position signal is an anomaly, and takes the form of a spike, as shown in FIG. 1B.
Accordingly, there is a need in the technology for a method and apparatus for providing servo information on a disk in a hard drive assembly while overcoming the aforementioned problems.